It is very important to think about home drainage concerns when you are designing landscape terraces, retaining walls, and flat grass areas, as well as slopes. The groundwater that builds up behind a retaining wall for instance is enough to force the wall over in time in between the saturation and freezing of groundwater. Typically this is a many decades process but eventually the new homeowners will take their turn at being the fall guys for the rest of the former home drainage procrastinator owners and be forced to solve the home drainage problem.
A retaining wall that is falling over is usually not something you notice happening. It happens over years. The wall can be pushed over in time with just the weight of the groundwater pushing on the retaining wall, especially in areas that freeze and thaw alot.
Hand excavated french drains installed above the retaining wall, about 18″ off the wall, with exposed river rock, in conjunction with weep holes at the base of the retaining wall and perhaps even hand excavated french drains at the base of the retaining wall as well are standards of retaining wall engineering. This duplicates the process most highway engineers use when building tall retaining walls along highways for instance. Many times french drains are installed at the base of the retaining wall in the beginning because these engineers know what groundwater does to retaining walls over years without them installed.
A hand excavated french drain can be installed at the base of a retaining wall as well but the one installed above the wall is the most important installation because if the french drain is clean and hand excavated and installed around 18″ from the foundation wall with a slope away from the retaining wall toward the french drain, the constant collection of groundwater near the retaining wall will starve the wall of rain water between the inside of the french drain and the retaining wall by flowing it away faster than it can soak in, thereby eliminating or reducing the hydrostatic pressure that causes the leaking of groundwater below grade.
A hand excavated french drain above the retaining wall can many times be daylight vented at the base of the wall as well if the bank being retained tapers down at the end of the retaining wall. All engineering concerns depend on the amount of grade drop needed and the length of the wall, and the degree of slope and height of bank being retained, as well as the soil conditions, whether fill or existing naturally compacted clay.
A quality french drain takes the hydrostatic pressure, caused by rain water saturation, off the back of the wall by creating a reduction or elimination of groundwater weight at the back of the retaining wall.
The french drain at the bottom of the retaining wall, along with weep holes bored in the concrete retaining wall, provide drainage from sources of groundwater that fill the back of the retaining wall at lower levels than surface levels, which actually is where you have an opportunity to catch that groundwater prior to it saturating and coming out again lower. Some groundwater just comes in lower, but even that groundwater identified as a spring is probably as a result of groundwater next to or above grade to the area showing the below grade groundwater entry. Cut off the groundwater feeding those areas and the so called spring dries up most often. If the retaining wall was built there knowing a year round spring was present, the question of whether that was a correct installation would come to my mind first off.
Retaining walls made of rock, boulders or wood all require the same protection from the same resulting groundwater problems and fall over faster when damaged than concrete retaining walls with key ways and footings poured with snap ties and wailers.
p> Flat grass areas look neat and proper but they can be sponges too. These flat areas many times have additions of humus and topsoil that when saturated turn into an absorbent sponge to hold rainwater and leak it below grade. This may be especially true on new home construction where the original top soil has been scraped off the site first in bulk and some topsoil and sod has been added.
Sod crushes flat when newly laid, until it has rooted. If those new sod areas get saturated with groundwater from any source, even what the family considers their required water schedule, the chance of an active family turning those areas into a real mess is always present and even likely. Always walk on plywood in areas that can be damaged by the traffic of workers feet and wheel barrows during french drain installations.
Some of those flat to low ground newly sodded areas are absolutely areas not to walk on for years when saturated unless yard french drains are installed through them with the sod replaced over the hand excavated french drains. Lots of work. A job for the professional in almost all cases for professional results. You won’t like the other results, trust me on that one.
Hand excavated french drains can be installed by cutting the sod, and running the french drain system through the grass or sod areas with the sod replaced over the weed, which covers the river rock in the french drain.
The sod can only be replaced in this fashion where fall or spring weather allows. The homeowner over seeds the french drain and drywell topped with dirt over weed cloth in the average installation for most of the year.
The objective here is to engineer at least a 2″ per l0 lineal foot drop in grade on the bottom of the aqua duct, on flat surfaces, that starts the hand excavated french drain installation. The bottom of the french drain must have a perfectly graded, flat shovel finished bottom, with no debris at all, containing a 3″ ads flex perforated pipe, 3/4″-1 1/2″ river rock, and weed cloth for groundwater. A ditch will not do. Therefore a ditch witch is not a tool with engineering experience or eyes and should never be used. Rain drain discharges installed are always plumbed with solid abs and ads pipe, usually 3″, so that roof water does not have to wind up mixing on the bottom of your french drain with the collected groundwater. This gives the french drain more capacity to handle groundwater as the roof water runs in solid pipe to the dry well.
Rain drain discharges to vent downspouts on your roof can be installed next to the perforated pipe on the bottom of the french drain which gives it grade to drain away faster than if installed flat on the outside of the foundation footing, where most systems are installed by builders, to the detriment of the homes drainage in time, as they plug up with no enhanced grade or aqua duct to run in. No debris or loose dirt what so ever is allowed in a quality french drain that is hand excavated. While sod replaced hand excavated french drains do not collect the groundwater as quickly as the exposed river, rock hand excavated french drains do they wick groundwater into the french drain system from the saturated soil around them for a distance of approximately 6-10 feet each side of the hand excavated french drain between the soil depths of 6″-18″ deep, which is where almost all the groundwater holds prior to it saturating deeper eventually.
Lawn french drain systems firm up the soil and reduce the hydrostatic pressure that causes soggy back yards and lawns that the kids cannot even play on without coming in trashed with mud. It is important to lay down 2 foot wide plywood runs to preserve the landscape and lawns during soil and sod removal as well as rock and perforated pipe installation. Cosmetic home drainage work is what feeds the bull dog, figuratively only folks, when working with high dollars properties and professional clients who want professional results. The sod should be cut with a hand sod cutter for best results and saved on a tarp and kept wet during installation until re-construction, if weather allows this without re-seeding. Get a utility locate prior as well to determine what you can do and where and know how to read it and how to excavate around gas, electric, cable tv, computer lines, sewer lines, water lines, sprinkler lines and other grade obstructions that require you to make a decision to either leave it or cut in out if it is in your desired hand excavated french drain aqua duct grade.